This invention relates to a process for producing improved metal containers for edibles and potable beverages. More specifically the invention relates to a process for producing metal containers with a thin protective silicone coating on the interior surface of the container. The invention also relates to improved metal containers having on the interior surfaces a cured phenylpolysiloxane resin coating.
It is known in the art of packaging edibles and potable beverages to fabricate metal containers from sheet metal precoated with thin protective layers. For example, the tin can is made from sheet steel coated with a thin layer of tin. Presently, aluminum metal with surfaces protected by organic resin coatings is also widely employed in fabricating containers for edibles and potable beverages. The organic resin coatings perform satisfactorily with many products, but with others, they do not adequately protect the packaged edibles and potable beverages. Beer in particular has been found to exhibit off-taste when packaged in contact with many organic coatings.
An improved interior coating for metal containers in which edibles and potable beverages are packaged, then, must meet a number of special requirements. Certainly, the coating must be sanitary and not deleteriously affect packaged products during long storage periods. The coating must resist the physical and chemical conditions of heat processing and pasteurizing the products in the container. Further, the coating must maintain its integrity and adhesion to the metal during mechanical operations of fabricating the interiorly-coated container from precoated metal stock.
Organosiloxane resin coatings have been used in contact with foodstuffs in applications such as cooking utensil coatings for food release as described in U.S. Pat. Nos. 3,300,542 and 3,632,794. In addition, a siloxane coating is described in Canadian Pat. No. 661,372 that improves the corrosion resistance of aluminum in contact with a mustard oil food product. The aluminum was coated with a solution of methyltriethoxysilane in xylene and heated at 500.degree. C. to 600.degree. C. for 5 minutes to cure the coating.
The cure system of the siloxane coating employed in the present invention is known from U.S. Pat. No. 3,344,104 which describes heat curable compositions containing (1) an organosilicon compound containing silicon-bonded hydroxyl radicals, (2) an organosilicon compound containing silicon-bonded alkoxy radicals and (3) an aldehyde or ketone. The cure system is described as especially useful for curing organosilicon compositions to coherent solids including silicone rubber.